1. Field of the Invention
The present invention relates generally to joints for surgical apparatus used in remote surgery, and more particularly to a roll joint for a surgical apparatus.
2. Description of Related Art
Minimally invasive telesurgical robotic systems increase a surgeon's dexterity when working within an internal surgical site, as well as allow a surgeon to operate on a patient from a remote location. In a telesurgery system, the surgeon is often provided with an image of the surgical site. While viewing a three-dimensional image of the surgical site on a suitable viewer or display, the surgeon performs the surgical procedures on the patient by manipulating master input devices of the system.
The master input devices control the motion of a servomechanically operated surgical instrument. During the surgical procedure, the telesurgical robotic system can provide mechanical actuation and control of a variety of surgical instruments or tools having end effectors such as tissue graspers, needle drivers, or the like. The end effectors allow the surgeon to perform various functions, e.g., holding or driving a needle, grasping a blood vessel, dissecting tissue, or the like, in response to manipulation of the master input devices.
Some surgical tools employ a roll-pitch-yaw mechanism for providing motion three degrees of freedom to an end effector through the use of three rotary joints. The pitch and yaw rotations are typically provided by a wrist mechanism coupled between a shaft of the tool and the end effector, and the roll rotation is typically provided by rotation of the entire shaft of the tool, driven by an actuator coupled to the proximal end of the shaft. At about 90° pitch, the yaw and roll rotational movements overlap, resulting in the loss of one degree of freedom of motion, referred to as a singularity.
Wrist mechanisms have been developed that can provide roll for the end effector distal to the pitch and yaw joints. These prior art roll joints used very small pulleys to transition the roll drive tendons from an axial orientation along the shaft of the surgical instrument to a perpendicular orientation suitable for actuating a rolling joint with an axis substantially parallel to the long axis of the surgical instrument. These pulleys required very small axles, which were limited in load carrying capability and were difficult to assemble. Further, these pulleys consumed a significant volume in the surgical instrument wrist in a manner that conflicts with making use of the same volume to stiffen the structure of the surgical instrument.